Shannen Doherty Says Her Cancer May Have Spread: "The Unknown Is the Scariest Part"

Shannen Doherty has revealed the heartbreaking news that her cancer may have spread.

"I had breast cancer that spread to the lymph nodes, and from one of my surgeries we discovered that some of the cancer cells might have actually gone out of the lymph nodes," the actress said in an exclusive interview yesterday with Entertainment Tonight. "So for that reason, we are doing chemo, and then after chemo, I'll do radiation."

The former Beverly Hills, 90210 star, 45, told People last summer that she'd been diagnosed with breast cancer in March 2015. Since then, she's had a single mastectomy and also undergone three of eight rounds of chemotherapy, which she described as being especially hard.

"You're throwing up every single second," she said. "After my first treatment I lost 10 pounds, instantly. You're throwing up and the last thing you want to do is be in a car. You don't want to be moved, you can't eat."

The actress's husband of five years, photographer Kurt Iswarienko, has been by her side during her treatments. "My husband has to, you know, pick me up," she said. "He puts me in the car, he buckles me in, and he drives me to my oncologist and they hook me up to an IV and I get hydrated."

When Doherty shaved her head last week, she credited her support system, including Iswarienko, her close friends, and mom Rosa, for helping her get through "an impossibly tough day."

"After my second treatment, my hair was really matted, like in dreadlocks. And I went to try and brush it out, and it just fell out," Doherty told ET. "I just remember holding onto huge clumps of my hair in my hands, and just running to my mom crying, like, 'My hair, my hair, my hair, my hair.'"

A photo posted by ShannenDoherty (@theshando) on Jul 25, 2016 at 10:26am PDT

Doherty documented the difficult process in a series of photos on Instagram—first cutting her hair into a pixie, then a mohawk, and finally shaving it completely. And although Iswarienko was in Mexico for work, he was still able to offer support.

"He was texting nonstop in the middle of his photoshoot like, 'Give me pictures, and are you OK? I wish I could be there,'" she said. "He was so stricken that he wasn't there with me but I sent him pictures and videos and he was like, 'Oh my God. You're hot with no hair.' So you know, everybody kind of made me feel better about it."

A photo posted by ShannenDoherty (@theshando) on Jul 19, 2016 at 9:05pm PDT

"Any time someone is told they have breast cancer, it's a very scary thing, emotionally and psychologically," Sharon Rosenbaum Smith, MD, a breast surgeon at Mount Sinai West in New York City, told Health. (Dr. Rosenbaum Smith has not treated Doherty.)

Based on Doherty's chemotherapy comments, Dr. Rosenbaum Smith says it's possible that the actress is experiencing particularly bad side effects. "Chemotherapy affects people in very different ways, and the side effects vary widely from person to person," she explains. "It sounds like unfortunately Shannen could be having a very severe reaction."

"We have a lot of great treatments out there for breast cancer and very good survival statistics," says Dr. Rosenbaum Smith. And even though these treatments can make patients feel extremely run-down, they're helping to fight the cancer cells and prevent them from coming back.

She adds: "The most important thing is to remember that hopefully this is a very short period in a very long life."

In the ET interview, Doherty said that "the unknown" has been the scariest part of having the disease. "Is the chemo going to work? Is the radiation going to work?" she said. "You know, am I going to have to go through this again, or am I going to get secondary cancer? Everything else is manageable. Pain is manageable, you know living without a breast is manageable, it's the worry of your future and how your future is going to affect the people you love."

Doherty's hope is that her story will help others who are fighting the same battle. "If I could help one person then it makes me go, 'Oh OK,'" she said. "It's easier to live with having cancer if I know I'm helping at least one person."